In solar power systems, energy is obtained by directly harnessing the electromagnetic solar radiation from the sun. The total solar radiation incident on the earth far exceeds the total power requirements well into the future and offers a viable offset to fossil fuels. Significant effort has been directed to higher utilization of solar energy but efficiency, space, and cost considerations have hampered this effort to date.
In applications such as digital photography, having a single focal-plane image array sensor, which can sense a broad spectrum is highly desirable. While sensing from Ultra Violet (UV), through the visible spectrum, and into the near and far infra red (IR) is required only for special applications, smaller spectral ranges of interest may be advantageously utilized.
The ability to provide light energy with controlled polarization is also desirable in the field of displays, to provide stereoscopic illusion of 3 dimensional space, colloquially related to as 3D.
Millimeter waves are radiant energy waves ranging from 30-300 GHz are used for detecting material differentiation purposes, and as a portion of hyperspectral imaging. The structures disclosed herein provide ability to detect or emit such waves with adaptations such as material selection and proper dimensioning. The term ‘radiant energy’ as used herein covers a very broad spectrum of radiation ranging from the Extremely High Frequency (EHF) with sub millimeter wavelength through the Infra Red (IR) and the visible spectrum, to the Ultra Violet (UV) at merely a few hundred nanometers. Oftentimes specific applications would be required to cover only portions of this spectrum, which forms their spectral range of interest. By way of example, for solar energy applications the spectral range of interest will likely be a spectrum containing most if not all of the solar spectrum available at the location where the solar cell is to be deployed, or the portion thereof which is economically used by the device at hand, typically 3 μm to 300 nm for example. The spectral range of interest for most display devices is within the visible light, even if some special application demand extending the spectral range. In some applications a specific wavelength may be desirably attenuated, such as by way of example reduction of blue light for aviation related devices. Yet, for devices directed to heat energy recovery, it is likely that only the infra-red portion of the spectral range is of interest. Similarly, the spectral range of interest may be applicable to portions of a device, for example a device may be directed to a broad spectrum, but portions thereof may be directed to a narrower spectrum, and the spectral range of interest is thus limited to the range of interest of the portion of the device. By way of a non-limiting example a television may occupy a display portion with a spectral range of interest including the visible range, while the device as a whole includes the aural range as well. It is seen therefore that the application at hand determines the spectral range of interest for which an apparatus utilizing the invention is directed to.
Therefore, the spectral range of interest is defined as relating to any portion or portions of the total available spectrum of frequencies which is being utilized by the application and or apparatus at hand, and which is desired to be detected and/or emitted utilizing the technologies, apparatuses, and/or methods of the invention(s) described herein, or their equivalents. The term spectral components as used herein means a portion of a broader spectrum, spatially separated from the broader spectrum by frequency and/or polarization.
The present invention is applicable to a very broad range of applications, and is selectively operational over a very broad spectrum of electromagnetic radiant energy, extending at least from the EHF to the UV, or any suitable spectral bands or domains. Therefore, for brevity and simplicity of expression, these specifications would relate to one example of the spectral range of interest, namely light, interchangeably with, and to denote, the spectrum described above, or portions thereof. Where specific constructs or conditions are more befitting specific portions of the spectrum such mention may be made. Similarly, terms such as optical, transparent, reflective, refractive and the like, should be construed to mean the appropriate equivalent terms befitting the specific portion of the spectrum at hand.
Structure to facilitate conversion of radiant energy to electricity or electrical signals (hereinafter “LE”), or conversion of electrical signals into radiant energy such as light (hereinafter “EL”) are known. Collectively, objects, materials, and structures which perform such conversion are referred to hereinunder as ‘converters’. By way of non-limiting examples, the term “converter” relates to light sources, light emitters, light modulators, light sensors, photovoltaic materials including organic and inorganic converters, quantum dots, photonic structures, and the like, CCD and CMOS structures, LEDs, OLEDs, LCDs, receiving and/or transmitting antennas and/or rectennas, phototransistors photodiodes, diodes, electroluminescent devices, fluorescent devices, gas discharge devices, electrochemical converters, and the like. The skilled in the art would recognize that certain LE converters may act as EL converters, and vice versa, with proper material selection, so a single converter may operate both as EL and LE converter, depending on the manner of operation. Alternatively converters may be built to operate only as LE or as EL converters. Furthermore, different types of converters may be employed in any desired combination, so the term converters may imply any combinations of LE and EL, as required by the application at hand.
Presently the most common structures for LE conversion are photovoltaic (PV) solar cells which generally use layers of different materials. In a PN based converter, a PN junction is formed at the interface of a positive and negative doped semiconductor materials, such as silicon. When exposed to a photon having energy equaling or higher than the band gap between the junction materials, the photon energy causes formation of electron-hole groups, which are separated and collected on both sides of the junction depletion zone.
Yet another class of converters employs polymer based photoabsorptive material as electron donors in combination with electron acceptors. In some cases the resulting excited electron is separated from the corresponding hole using different work function conductors. In other cases, a polymer electron acceptor forms a heterojunction with the electron donor. Such converters generally are less expensive than PV converters, but have lower efficiency therefrom; however, their efficiency may be significantly advanced by aspects of the present invention. Notably, the PN junction of semiconductor-based converters is treated as comprising electron acceptor and electron donor materials respectively, regardless of the actual mechanism by which charges are separated therein.
Other types of converters utilize antennas, and more commonly rectennas, to achieve the energy conversion. The term rectenna relates to an antenna structure having a rectifier integrated with, or closely coupled to, the antenna, such that electromagnetic energy incident on the antenna is rectified and presented as primarily unidirectional (ideally DC) signal. By way of example, rectennas are described in U.S. Pat. No. 7,799,998 to Cutler, and in “Nanoscale Devices for Rectification of High Frequency Radiation from the Infrared through the Visible: A New Approach”, N. M. Miskovsky, P. H. Cutler, A. Mayer, B. L. Weiss, BrianWillis, T. E. Sullivan, and P. B. Lerner, Journal of Nanotechnology, Volume 2012, Article ID 512379, doi:10.1155/2012/512379, Hindawi Publishing Corporation©. which is incorporated herein by reference in its entirety.
LE converters typically employ a broad-band collector. Photovoltaic converters are high pass collectors in that all energy above a critical cutoff frequency is converted. However, the photon energy in excess of the band gap energy is converted to heat. Rectenna converters attempt to employ broad-band antennas with rectifiers. Their operating frequency is limited by the characteristics of the rectifier and by the bandwidth of the antenna. However, converters generally exhibit a frequency dependent optimum efficiency, which is commonly also affected by temperature.
Waveguides are a known structure for trapping and guiding electromagnetic energy along a predetermined path. An efficient waveguide may be formed by locating a layer of dielectric or semiconducting material between cladding layers on opposite sides thereof. The cladding may comprise dielectric material or conductors, commonly metal. Waveguides have a cutoff frequency, which is dictated by the wavelength in the waveguide materials, and the waveguide width. As the frequency of the energy propagating in the waveguide approaches the cutoff frequency Fc, the energy propagation speed along the waveguide is slowed down. The energy propagation of a wave along a waveguide may be considered as having an angle relative to cladding. This angle is determined by the relationship between the wavelength of the wave and the waveguide width in the dimension in with the wave is being guided. If the width of the waveguide equals one half of the wave wavelength, the wave reaches resonance, and the energy propagation along the waveguide propagation axis stops. The condition where energy is at or close to such resonance will be termed as a stationary resonant condition.
In these specifications “semiconductor” will be used to denote a photovoltaicly active material, having a bandgap comparable to or smaller than the photon energy of any photon in the spectrum of interest to a specific application.
In contrast, a transparent conductor is a material having a comparatively small but meaningful conductivity due to a partially filled conduction band or partially empty valence band but having a band-gap between the valence band and conduction band exceeding the energy of any photon in the spectrum of interest. These materials act like a dielectric at high frequencies but act like a conductor at low frequencies. Transparent dielectric materials also have low optical losses such that photons efficiently transmit through such material, at least at the spectrum of interest or a significant portion thereof.
While transparent conductors may be considered as wide bandgap semiconducting materials, they are used as conductors in most applications. Dielectrics, transparent conductors, and semiconductors, as used in these specifications, refer to materials that have a dielectric constant at optical frequencies; however, the distinction between a semiconductor and the remaining materials is that the bandgap of a semiconductor is not substantially larger than the photon energy. As a general and non-limiting guideline, table 1 describes several characteristics of the different conductive, insulating, and semi-conductive materials.
TABLE 1MaterialSemi-MetalTrans. Cond.conductorDielectricBandgap→ 0>>photon≦photon>>photonDC ConductivityhighgoodVaries→ 0Optical PropertyreflectivetransparentabsorptivetransparentDielectric constantcomplexlow losslossylow loss
Radiant energy converters typically employ normal incidence of radiant electromagnetic energy onto a detection structure. Normal incidence has the limitation of a comparatively small probability of being utilized for energy conversion before being transmitted through the collection layer. Energy transmitted through the collection layer is, at best, lost and, at worst, converted to heat in the supporting substrate. Several attempts have been made to provide converters that use “side illumination” in which the light is inserted from the side of the junction. Such examples include, inter-alia, in U.S. Pat. No. 3,422,527 to Gault, U.S. Pat. No. 3,433,677 to Robinson, and U.S. Pat. No. 4,332,973 to Sater.
Prisms and other refractive devices can be used to improve incidence angles, and to direct different frequencies of radiant energy to different regions of a converter, where each region is optimized for a target frequency. U.S. Pat. No. 7,888,589 to Mastromattteo and U.S. Pat. No. 8,188,366 to Hecht, disclose examples of such devices.
Continuous Resonant Trap refractors (CRTR) and lateral waveguides (generally referred to in these specification as ‘stacked waveguides’) were first disclosed in U.S. Provisional Patent Application 61/701,687, titled “Continuous Resonant Trap Refractor, Waveguide-based Energy Converters, Energy Conversion Cells, and Display Panels Using Same” filed Sep. 16, 2012. Applications of CRTR structure and lateral waveguides, and further refinements thereto are disclosed in U.S. Patent Applications 61/713,602, titled “Image Array Sensor”; 61/718,181, titled “Nano-Scale Continuous Resonance Trap Refractor”; 61/723,832, titled “Pixel Structure Using Tapered Light waveguides, Displays, Display Panels, and Devices Using Same”; 61/723,773, titled “Optical Structure for Banknote Authentication”; Ser. No. 13/726,044 titled “Pixel Structure Using Tapered Light waveguides, Displays, Display Panels, and Devices Using Same”; Ser. No. 13/685,691 titled “Pixel structure and Image Array Sensors using same”; all to Andle and Wertsberger; and U.S. provisional Patent Application 61/724,920, titled “Optical Structure for Banknote Authentication, and Optical Key Arrangement for Activation Signal Responsive to Special Light Characteristics”, to Wertsberger. Each of the above identified Patent Applications is incorporated herein by reference in its entirety.
There is therefore a clear, and heretofore unanswered, need for higher efficiency converters and converter arrangements for converting radiant energy to electrical energy, and vice versa. The present invention aims to provide such a solution.